Process of producing rolled stock from a high-melting metal by continuous casting and rolling operations



Jan.,27,1 970 B TARMANN ETA'Lw 3,491,824

PROCESS OF PRODUCI NG ROLLED STOCK FROM A HIGH-MELTING METAL BY CONTINUOUS CASTING AND ROLLING OPERATIONS Filed Dec. 28, 1966 mvzmons; Bmu'na TFIRMRNN Hel'nrlal. VONGHNK ATTORNEY United States Patent US. Cl. 16476 4 Claims ABSTRACT OF THE DISCLOSURE This disclosure relates to a process in which a highmelting metal is subjected to continuous casting and rolling operations. The rolling operation is performed at a point where the casting would contain a molten core having a thickness of 5-30 mm. without such rolling operation. The velocity of the casting is measured closely before the rolling station and behind the rolling station. The measured velocities and the predetermined crosssectional areas of the casting at the measuring points are used to derive an indication of the proportion of the molten core closely before the rolling station. The process is controlled so that the tip of the molten core is shifted by the rolling operation to a point which closely precedes the rolling station.

According to a related process, which is described in our co-pending application Ser. No. 586,494, a plant for continuous casting is succeeded by a shaping device for shaping the solidified cross-section of the continuous casting at a location where the thickness of the molten core is 5-30 millimeters, irrespective of the cross-sectional area of the casting. In that proposal it is essential that a single shaping step at that location should reduce the length of the molten core so that the tip of the core precedes the plane in which the casting assumes a reduced cross-section, which is determined by the setting of this shaping device.

It has been reported that said proposal results in improved properties as regards surface quality and internal flaws.

In carrying out said related process in a given plant, the operating conditions must be adjusted so that the cross-sectional area before the beginning of the deformation is maintained constant and within the desired dimensional range. In a given plant and with a simple casting program, this adjustment generally does not involve difficulties that cannot 'be overcome because it is sufiicient to ascertain the proper conditions once and the same conditions can be adopted in further runs.

On the other hand, if an existing plant is to be used for making castings which dilfer in cross-sectional size and cross-sectional shape and if difiFerent kinds of steel are to be cast, the operating conditions must be adjusted in each case. For this reason a process would be desirable in which the operating conditions required to obtain a predetermined crossseetion of the molten core at the location which is critical for the described shaping process can be adjusted in a simple manner.

The single shaping step of the process described in our co-pending application Ser. No. 586,494 must be carried out at a location of the continuous casting where the molten core would otherwise have a thickness of 5-30 millimeters and the as-cast cross-section of the casting and the dimensions of the roll nip to provide a desired final cross-section are pre-given.

According to the invention, the velocity of the material before and after the shaping is measured, the actual proportion of the molten core is ascertained from the result of such measurement, and the operating conditions are adjusted to obtain a molten core in the pre-given proportion.

The invention will be explained more fully with reference to the accompanying drawing in which FIGS. 1 and 2 are diagrammatic views showing apparatus for carrying out the process according to the invention.

With reference to FIG. 1, a continuous casting withdrawn from a mold 3 is moved by and between a pair of rolls 5. Sensing units 1 and 2 serve for measuring the velocity of the continuous casting before and after its shaping by the pair of rolls 5. If the casting had completely solidified before being subjected to the single shaping step by the pair of rolls 5, the product of the cross-Sectional area of the material and the velocity of the material would be the same before and behind the pair of rolls 5. If there is a molten core at the entrance to this pair of rolls, the above-mentioned product must be larger before said pair of rolls than behind the same. The same applies if there is a molten core before and behind the pair of rolls; in this case the velocity of the material before and after the shaping would be the same or approximately the same. With pre-given dimensions of the cross-section of the casting withdrawn from the mold and of the roll nip, and consequently with constant dimensions of the shaped casting, the above-mentioned velocity measurements permit of a conclusion as to the proportion of the molten core immediately before the shaping.

For instance, if a continuous casting having in its ascast state a cross-section of 120 millimeters square is allowed to solidify completely before it is shaped in a single step to a cross-section of 120 mm. x mm. and is lowered from the mold at a velocity of 2 meters per minute, the velocity of the casting behind the shaping device 5 will be 3 meters per minute. On the other hand, if the casting contains a molten core which is 25 millimeters in diameter, corresponding to 3.5% of the crosssectional area, and the casting is lowered from the mold also at a velocity of 2 meters per minute, the velocity of the casting behind the shaping device will be 2.895 meters per minute or 3.5 that of the casting which had been shaped after complete solidification.

The molten proportion F expressed as a percentage of the cross-sectional area of the casting, may be calculated, e.g., by the equation F -percent= f ,100

where v is the velocity of the material of the casting having the as-cast cross-sectional area F and v is the velocity of the material of the resulting rolled :billet having a cross-sectional area F With castings having round or square as-cast crosssections and a molten core which is circular in crosssection, the diameter or thickness of the circular molten core can easily be calculated from F percent. With castings having other as-cast cross-sections, the cross-sectional shape of the molten core must be taken into account. For instance, the molten core has an approximately rectangular cross-sectional shape in slab castings.

If the above-mentioned calculations show that the proportion of the molten core is outside the desired range, the operating conditions must be changed. If the proportion of the molten core is too large, the velocity at which the casting is lowered from the mold must be reduced, if the cooling rate remains the same, or the cooling rate must be increased, if the velocity at which the casting is lowered from the mold remains the same. On the other hand, if the proportion of the molten core 'is too'small,

the velocity at which the casting is lowered from the mold must be increased, if the cooling rate remains the same, or the cooling rate must be reduced, if the velocity remains the same. Both factors may be appropriately changed at the same time.

The previously known methods of ascertaining the cross-section of the molten core cannot be used for continuous measurements during operation and for a utilization of such measurements for controlling the operating conditions. An example of such method is a sensing of the molten core with the aid of radio-active isotopes. In this case, radiographs of the casting must be made. Another method comprises filling-the tip of the molten core with low-melting metals which have a higher specific gravity than the casting, e.g., with lead. In this case the casting must be cut through for ascertaining the tip of the molten core. Further methods of ascertaining the proportion of the molten core are the measuring of the thickness of the shell with ultrasonics-in this case it is difficult to introduce the sound waves into the hot castingor a penetration of the casting with gamma rays this method cannot be used in commercial operation because the differential absorption due to the different states of matter is too small.

According to the invention, the thickness of the molten core is ascertained by a measurement of two velocities of the material. Compared to the previously proposed methods, this suggestion has the advantage that it is highly accurate and sufficiently safe and can easily be carried out.

The velocity of the material can be sensed in known manner with mechanical or optical methods of measurement.

FIG. 2 shows an apparatus for carrying out another embodiment of the process according to the invention. The same reference characters are used for parts corresponding to those in FIG. 1.

Under comparable conditions, the accuracy with which the thickness of the molten core is ascertained according to the invention will be increased if the difference between the velocities v and v of the material is increased. For this reason, where a'plurality of pairs of rolls 5, 6, 7, 8 are consecutively arranged in the direction of the axis of the casting and used for shaping the casting, as is shown in FIG. 2, it is desirable to measure the velocity v of the casting having left the last pair of rolls 8 so that the casting has the final cross-section F 'of the .rolled product, and to utilize the result of this measurement in the above-mentionedvmanner for ascertaining the proportion of the molten core. The velocity v is sensed with the sensing unit 1. Obviously, the velocity v may be sensed behind any other pair of rolls and th measured value may be combined with the cross-section P of the material behind this pair of rolls. This combination may be effected, e.g., with the aid of the above-mentioned equation.

What is claimed is:

1. A process of producing rolled stock made from a high-melting metal, which comprises forming a continuous casting of said metal, which casting has a predetermined cross-section and contains a molten core, moving said continuous casting along a predetermined path at a controlled velocity, cooling said continuous casting at a controlled rate, subjecting said casting to deformation by rolling to impart to said casting a reduced cross-section at a location of said path where the thickness of said molten core would be 5-30 millimeters without such deformation and under the same conditions in other respects, measuring the velocity of said casting at two points of measurement respectively disposed closely before said location and behind said location, and measuring the crosssectional areas of said casting at said points of measurement to obtain an indication of the proportion of the molten core at said point of measurement disposed before said location, and controlling said process in response to said measurements by adjusting at least one adjustment of the group of adjustments comprising the step of adjusting the cooling rate and the step of adjusting the casting velocity of said continuous casting, so that said deformation is sufficient to shift the tip of said molten core to a point which closely precedes said location, considered in the direction of movement of said casting.

2. A process as set forth in claim 1, in which said high-melting metal is selected from the class consisting of plain carbon steels and alloy steels.

3. A process as set forth in claim 1, in which said casting is subjected to deformation by rolling at least at one additional point between said location and said point of measurement which is disposed behind said location.

4. A process as set forth in claim 1, in which the location and amount of said deformation are maintained constant and the quantity of heat extracted from said casting before said location is varied to control the proportion of said molten core at said point of measurement disposed before said location.

References Cited UNITED STATES PATENTS 494,659 4/1893 Very l64283 X 2,519,818 8/1950 Blain 729 2,851,911 9/1958 Hessenberg 729 3,237,251 3/ 1966 Thalmann 164-4 3,270,376 9/1966 Thalmann l644 3,307,230 3/1967 Goss 164-281 J. SPENCER OVERHOLSER, Primary Examiner R. SPENCER ANNEAR, Assistant Examiner US. Cl. X.R. l6482 

